如何在 LINQ 中获取查询"remainder"(所有不匹配的对)并将其收集到列表中

Question

我将请求与基于requesttid的响应进行匹配，如下所示:

    public void MatchCallPairsByRequestId()
    {
        // Finds request that have matching response based on RequestId and create callpair
       _callPairs = _requests.Where(req => !string.IsNullOrEmpty(req.RequestId))
                  .Join(_responses, 
                        req => req.RequestId,
                        resp => resp.RequestId,
                        (req, resp) => new CallPair(req, resp)).ToList();
    }

或在LINQ表达式:

 _callPairs = (from req in _requests
                  join resp in _responses
                      on req.RequestId equals resp.RequestId
                      where !string.IsNullOrEmpty(req.RequestId)
                  select new CallPair(req, resp)).ToList();

现在我想在一个名为nonMatchedRequests和nonMatchedResponses的单独列表中收集与函数不匹配的请求和响应。如何使用此查询在单独的列表中收集其余部分?

Answer 1

我不确定是否有一种方法可以在一次调用中完成此操作，或者甚至可以将其与生成配对列表合并，但是您可以运行几个后续方法来确定不匹配的项:

var unmatchedRequests = _requests.Except(_callPairs.Select(cp => cp.Request));
var unmatchedResponses = _responses.Except(_callPairs.Select(cp => cp.Response));

Enumerable.Join的文档还谈到了能够使用GroupJoin执行外部连接，如这里所述，这将返回不匹配的请求，尽管我认为它会错过不匹配的响应。

^{我屏住呼吸等待答案演示linq魔法，更有效地完成这个调用}

Answer 2

你可能可以通过.Except()来做到这一点，也许还可以对不同的值进行操作

// Matching pairs
_callPairs = _requests.Where(req => !string.IsNullOrEmpty(req.RequestId))
    .Join(
        _responses, 
        req => req.RequestId,
        resp => resp.RequestId, 
        (req, resp) => new CallPair(req, resp)
    ).ToList();
// To use the .Distinct() part, you're going to need to implement IEqualityComparer twice
// Easy but maybe not strictly necessary, no matter what it would be a solid approach
var matchedRequests = _callPairs.Select(cp => cp.Request); //.Distinct(new RequestComparer());
var matchedResponses = _callPairs.Select(cp => cp.Response); //.Distinct(new ResponseComparer());
var nonMatchingRequests = _requests.Except(matchedRequests);
var nonMatchingResponses = _responses.Except(matchedResponses);

Answer 3

查找返回的CallPair对象中不存在的请求和响应

var unmatchedRequests = _requests.Where(req => !_callPairs.Any(cp => cp.Request == req));
var unmatchedResponses = _responses.Where(resp => !_callPairs.Any(cp => cp.Response == resp));

编辑:这里是一些示例代码

var requests = Enumerable.Range(0, 10).Select(i => "Request" + i).ToList();
var responses = Enumerable.Range(0, 10).Select(i => "Response" + i).ToList();
var pairs = Enumerable.Range(0, 3).Select(i => new KeyValuePair<string, string>("Request" + i, "Response" + i * 2)).ToList();
var unmatchedRequests = requests.Where(req => !pairs.Any(cp => cp.Key == req));
var unmatchedResponses = responses.Where(resp => !pairs.Any(cp => cp.Value == resp));

我得到7个不匹配的请求和7个不匹配的响应，这看起来是正确的。您的一些请求是否会被匹配到多个响应，反之亦然?